Voltage spike indication

C

chevelle

Filing Flight Plan
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flyingfarmer
I get voltage spike on my mk12d when I transmit. The other comm is fine just the mk12d. Any ideas
 
chevelle said:
I get voltage spike on my mk12d when I transmit. The other comm is fine just the mk12d. Any ideas
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Where is this spike showing up? On the airplane's voltmeter? A spike is by definition a very sharp and brief and fairly large rise in voltage. You need an oscilloscope to see it. Voltmeters are seldom fast enough to show anything. So I'm guessing you're seeing a bit of a rise on the airplane's voltmeter or ammeter or load meter, and there is one possible cause I can think of for that. You have an electronic alternator control unit (ACU) or electronic regulator, and there is a leaky ground connection at one end or the other of the antenna cable shielding for that com. RF escapes, gets into the airplane's wiring and messes with the primitive brain in that ACU and causes it to briefly increase the alternator's field current, increasing the alternator output for a very short time. In some airplanes that have an overvolt sensor, this will cause the ACU to shut the alternator off. The old electromechanical regulators were pretty much immune to this since they drew a lot more reference current and would suppress such a interference.

I'd start by checking the bayonet cable connector at the antenna base in the cabin ceiling. That's where condensation gets at the connection and causes corrosion and breakdown of the grounding of the shield.

Leaky antenna cable connections can also trigger the ELT when you hit the push-to-talk. The RF gets into the ELT remote wiring.
 
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